1. Field of The Invention
The present invention relates to an improvement of a drive system of a hybrid vehicle.
2. Description of Related Art
There is known a drive apparatus of a hybrid vehicle including: a differential device which comprises a first differential mechanism and a second differential mechanism and which includes four rotary components; and an engine, a first electric motor, a second electric motor and an output rotary member, which are respectively connected to the four rotary components, and wherein one of the four rotary components consists of a rotary element of the first differential mechanism and a rotary element of the second differential mechanism which are selectively connected to each other through a coupling element. JP-2013-39906 A1 discloses an example of such hybrid vehicle drive apparatus, which can be selectively placed in a plurality of vehicle drive modes according to respective different combinations of operating states of a plurality of coupling elements.
In the prior art hybrid vehicle drive apparatus described above, a drive system of a hybrid vehicle is temporarily placed in an off state (“Ready-OFF” state), and is then re-started, namely, restored to an on state (“Ready-ON” state), according to a running condition of the hybrid vehicle. When the above-described coupling element for selectively connecting the rotary elements of the first and second differential mechanisms is brought into an engaged state upon re-starting of the drive system, there is a risk of deceleration of the hybrid vehicle felt by its operator due to a difference between rotating speeds of the two rotary elements. This problem was first discovered by the present inventors in a process of an intensive study in an effort to improve the performance of the hybrid vehicle.